Algebra - Ch. 9: Solving Word Problems with Factoring (9 of 17) Example 9

In this video I will find at what time will the projectile reach a height of 156ft if the height gained by a projectile that is fired straight up can be expressed in terms of t seconds: h=128t-16t^2.

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[aliso-pvll]

Doc, Listening to your explaination of the projectile height and maximum height, and never taken a physics course, is the height in feet(156ft) the point in which the projectile begins to decelerate and gravity is not more than the acceleration of the projectile until it reaches maximum height? Then the projectile stops for a moment in time then begins to fall downward and reaches the 156ft in the time you expressed? Thanks for your fine videos.

[amandajin]

can you help me solve this problem?


3x-9=x-9/3
prove is: 3x-9=0 x-9/3=0
3x=9 x=9/3
x=9/3 x=3
x=3
BUT when you put actual number the answer is not the same.
eg: if x=2
3x-9=0 x-9/3=0
3(2)-9 (2)-3
=6-9 =-1
=-3
is 3x-9 equal to x-9/3 ???